Abstract
Flavonoids, a subclass of polyphenols, have been shown to be effective against several types of cancer, by decreasing proliferation and inducing apoptosis. Therefore, the aim of the present study was to assess the anti-carcinogenic potential of luteolin on HeLa human cervical cancer cells, through the use of a cell viability assay, DNA fragmentation assay, mitochondrial membrane potential assay, cell cycle analysis using Annexin/PI staining and flow cytometry, gene expression analysis and a protein profiling array. Luteolin treatment exhibited cytotoxicity towards HeLa cells in a dose- and time-dependent manner, and its anti-proliferative properties were confirmed by accumulation of luteolin-treated cells in sub-G(1) phases. Cytotoxicity induced by luteolin treatment resulted in apoptosis, which was mediated through depolarization of the mitochondrial membrane potential and DNA fragmentation. Furthermore, luteolin treatment increased the expression of various proapoptotic genes, including APAF1, BAX, BAD, BID, BOK, BAK1, TRADD, FADD, FAS, and Caspases 3 and 9, whereas the expression of anti-apoptotic genes, including NAIP, MCL-1 and BCL-2, was decreased. Cell cycle regulatory genes, including CCND1, 2 and 3, CCNE2, CDKN1A, CDKN2B, CDK4 and CDK2, were decreased following treatment. Expression of TRAILR2/DR5, TRAILR1/DR4, Fas/TNFRSF6/CD95 and TNFR1/TNFRSF1A, as well as pro-apoptotic proteins, including BAD, BAX and Cytochrome C were consistently increased, and the expression of antiapoptotic proteins, HIF1 alpha, BCL-X, MCL1 and BCL2, were found to be decreased following treatment. Expression of AKT1 and 2, ELK1, PIK3C2A, PIK3C2B, MAPK14, MAP3K5, MAPK3 and MAPK1 was significantly decreased at the transcriptional level. Expression of GSK3b (p-ser9), PRAS 40 (p-Ther246), BAD (p-ser112), PTEN (p-ser380), AKT (p-ser473), ERK2 (p-Y185/Y187), RISK2 (p-ser386), P70S6k (p-Thr421/ser424), PDK1(p-ser241), ERK1 (p-T202/Y204) and MTOR (p-ser2448) was downregulated and expression of P53 (p-ser241) and P27(p-Thr198) was upregulated by luteolin in a dose-dependent manner, indicating its anti-proliferative and apoptosis enabling properties, and this may have been mediated via inhibition of the AKT and the MAPK pathways.